Android如何创建可拖动的图片控件

package com.example.timertest; 
 
 
import java.util.ArrayList; 
import android.annotation.SuppressLint; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.Canvas; 
import android.graphics.Paint; 
import android.graphics.PointF; 
import android.graphics.Rect; 
import android.graphics.RectF; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.WindowManager; 
 
@SuppressLint("ClickableViewAccessibility") 
public class DragImageView extends View{ 
   
  private Bitmap bmp = null; 
  private PointF orgPos = new PointF(0, 0); 
  private PointF downPos = new PointF(0, 0); 
  private PointF movePos = new PointF(0, 0); 
  private boolean bMove = false; 
  private int nDstWidth = 0; 
  private int nDstHeight = 0; 
  private Rect rcSrc = new Rect(0, 0 , 0, 0); 
  private RectF rcDst = new RectF(0, 0, 0, 0); 
  private Paint paint = null; 
  public DragImageView(Context context) { 
    super(context); 
    // TODO Auto-generated constructor stub 
    paint = new Paint(Paint.ANTI_ALIAS_FLAG); 
    //setOnClickListener(new DivOnClickListener()); 
    //setOnTouchListener(l); 
  } 
   
  public DragImageView(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    //bmp = img; 
    paint = new Paint(Paint.ANTI_ALIAS_FLAG); 
  } 
  public DragImageView(Context context, AttributeSet attrs, int defStyleAttr){ 
    super(context, attrs, defStyleAttr); 
    paint = new Paint(Paint.ANTI_ALIAS_FLAG); 
  } 
   
  public void SetImage(Bitmap img){ 
    if ( bmp != null ){ 
      bmp = null; 
    } 
    bmp = img; 
  } 
 
  @Override 
  public void addTouchables(ArrayList views) { 
    // TODO Auto-generated method stub 
    super.addTouchables(views); 
  } 
 
  @Override 
  public boolean onTouchEvent(MotionEvent event) { 
    // TODO Auto-generated method stub 
    float fPosX = event.getX(); 
    float fPosY = event.getY(); 
    int nAct = event.getAction(); 
    switch ( nAct ){ 
    case MotionEvent.ACTION_MOVE:{ 
      if ( !bMove ) 
        bMove = true; 
      movePos.x = fPosX - downPos.x; 
      movePos.y = fPosY - downPos.y; 
      downPos.x = fPosX; 
      downPos.y = fPosY; 
      invalidate(); 
    } 
      break; 
    case MotionEvent.ACTION_DOWN:{ 
      downPos.x = fPosX; 
      downPos.y = fPosY; 
    } 
      break; 
    case MotionEvent.ACTION_UP: 
      break; 
    } 
    //一定要返回ture，如果返回父类方法即false，则后续的move up 消息都不会触发。 
    return true; 
    //return super.onTouchEvent(event); 
  } 
 
  @Override 
  protected void onDraw(Canvas canvas) { 
    // TODO Auto-generated method stub 
    super.onDraw(canvas); 
    if ( bmp == null ) 
      return ; 
    int nWidth = bmp.getWidth(); 
    int nHeight = bmp.getHeight(); 
    if ( !bMove ){ 
      orgPos = GetCenterPos(); 
    } 
    else{ 
      orgPos.x += movePos.x; 
      orgPos.y += movePos.y; 
    } 
    rcSrc.right = nWidth; 
    rcSrc.bottom = nHeight; 
    rcDst.left = orgPos.x; 
    rcDst.top = orgPos.y; 
    rcDst.right = orgPos.x+nDstWidth; 
    rcDst.bottom = orgPos.y+nDstHeight; 
    canvas.drawBitmap(bmp, rcSrc, rcDst, paint); 
  } 
   
  protected PointF GetCenterPos(){ 
    PointF pt = new PointF(0, 0); 
    if ( bmp == null ) 
      return pt; 
    WindowManager wm = (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE); 
    //wm.getDefaultDisplay().getSize(pt); 
    int nScrWidth = wm.getDefaultDisplay().getWidth(); 
    @SuppressWarnings("deprecation") 
    int nScrHeight = wm.getDefaultDisplay().getHeight(); 
    int nWidth = bmp.getWidth(); 
    int nHeight = bmp.getHeight(); 
    float fImgRate = nWidth/(float)nHeight; 
    float fScrRate = nScrWidth/(float)nScrHeight; 
    if ( nWidth>nScrWidth && nHeight>nScrHeight ){ 
      if ( fImgRate > fScrRate ){ 
         
        nDstWidth = nScrWidth; 
        nDstHeight = (int)(nScrWidth/fImgRate); 
 
      } 
      else{ 
         
        nDstHeight = nScrHeight; 
        nDstWidth= (int)(nScrHeight*fImgRate); 
   
      } 
    } 
    else if ( nWidth>nScrWidth ){ 
      nDstWidth = nScrWidth; 
      nDstHeight = nHeight; 
    } 
    else if ( nHeight>nScrHeight ){ 
      nDstWidth = nWidth; 
      nDstHeight = nScrHeight; 
    } 
    else{ 
      nDstWidth = nWidth; 
      nDstHeight = nHeight; 
    } 
    pt.y = (nScrHeight-nDstHeight)/2.0f; 
    pt.x = (nScrWidth-nDstWidth)/2.0f; 
    return pt; 
  } 
   
 
}